Brake fluid

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Motul DOT 5.1 brake fluid

Brake fluid is used for hydraulics of brakes pushed though master cylinder enforced by vacuum booster. So having enough amount of brake fluid and could be critical for safety and performance. There are several types of brake fluids differs by boiling temperature and composition: DOT 3, DOT 4, DOT 5 and DOT 5.1.

Performance

Boiling temperature
Type Dry boiling point Wet boiling point
DOT 3 205 °C / 401 °F 140 °C / 284 °F
DOT 4 230 °C / 446 °F 155 °C / 311 °F
DOT 5 260 °C / 500 °F 180 °C / 356 °F
DOT 5.1 260 °C / 500 °F 180 °C / 356 °F

Composition

DOT 5 is the only from the list which is silicon-based, DOT 3, DOT 4 and DOT 5.1 are polyethylene glycol-based. So there could be different requirements for rubbers on using DOT 5 and DOT 5.1 in spite of the same performance values.

One more difference between silicon-based brake fluids(DOT 5) and polyethylene glycol-based ones(DOT 3, DOT 4, DOT 5.1) - silicon-based are not hydroscopic which means it would not try to absorb water from the air.

Stock recommendations

As a stock for Nissan 350z/G35 and the whole family Nissan recommends to use DOT 4 which is not such a bad choice for street driving. For track usage it would be smarter to use DOT 5.1 with Akebono brake kit or Brembo Gold and armored brake lines to keep the pressure and utilise higher boiling temperature.